1. Field of the Invention
The invention concerns an addressable photodetector array enabling a subscriber to select one of a number of optical signals each emitted by a separate light source, for example an optical fiber delivering an analog or digital signal, each light source illuminating a photodetector of the array.
2. Description of the Prior Art
Matrix photodetector arrays are already known, in particular from French Pat. Nos. 2 441 309 and 2 445 678. Each row is connected to a common output channel through a transistor which is turned on by a voltage applied to its grid by means of a row select control line, and each photodetector is connected to a row through a transistor; all the transistors assigned to all the photodetectors in the same column have their grid connected to a column control line; a control voltage applied to the column control line thus provides for connecting the photodetector in the column corresponding to the selected line. When the photodetector thus selected receives a light signal, a current flows in the common output channel. In a photodetector array of this kind, the unselected photodetectors cannot conduct away the charges created when they receive an optical signal since the transistors which connect them to the rows are normally turned off except for those of the selected column; it is therefore necessary that the transistors connecting the rows to the common output channel be actually turned off, which requires that their leakage current be zero or very low so as not to transmit the current from the photodetectors of the selected column, or the current from the photodetectors of the other columns if the transistor which connects each of them to a row is not turned off, that is if its leakage current is not zero or very low; in the case of the photodetectors forming part of the selected row, their current would disturb the current from the selected photodetector if the transistor which connects each of them to said row is not turned off.
An objective of the present invention is an addressable photodetector array which does not have the disadvantages of the known array and which can be readily implemented in integrated circuit form.